A stepper motor is a brushless electric motor that is used when fine and controlled motion is required. A stepper motor can separate a full revolution into a large number of steps. Stepper motors may be designed in a variety of ways; however, the general theme leading to their precise control is an array of poles located on a rotor shaft. The rotor shaft is surrounded by a series of electromagnets. When one electromagnet is energized, the shaft rotates to align a pole with the energized electromagnet. This allows the shaft to rotate in a series of discrete angular intervals, or steps, with one step being taken each time a command pulse is received.
The position of a stepper motor can be controlled without any feedback mechanism. When a definite number of pulses have been supplied, the shaft will have turned through a known angle. This makes the motor ideally suited for open-loop position control.
Stepper motors are used in a wide variety of positioning systems. Their precise control causes stepper motors to be commonly used in computer numerical control (CNC) machines, printers, floppy disk drives, and many other machines.
In certain applications, when the stepper motor is not energized, it becomes critical to recognize the angular position of the rotor. For instance, in industrial controls, as part of a configuration, the position of knobs can be set by a user once and the device could be expected to move the knobs to the corresponding positions whenever the same configuration is reloaded. Typically, this is made feasible by coupling a stepper motor to an optical encoder to form what is conventionally called an integrated stepper motor. The position of the knobs under the physical command of a user is observed by receiving feedback from the encoder.
FIG. 1 is a block diagram illustrating a conventional integrated stepper motor. The integrated stepper motor comprises a conventional stepper motor with an external encoder coupled to the motor shaft. The external encoder may commonly be an optical encoder or a magnetic flux based encoder.
FIG. 2 illustrates an external view of a conventional integrated stepper motor. The figure illustrates how an external encoder may be coupled to the shaft of a stepper motor in order to capture the rotor's motion when being manually turned.
Using an external encoder in conjunction with a stepper motor has several drawbacks. The external encoder can be expensive and dramatically increase the cost of the device. Additionally, the extra component takes up space, which may be at a premium if the device is to be used in small scale application. Finally, the addition of external hardware increases the chances of device failure due to wear and tear.